This invention relates to a low cost drug delivery system useful in delivering drugs, from pliable plastic containers.
Many drugs in the healthcare field are administered to a patient on a continuous basis. Continuous delivery of a drug to a patient was initially achieved by placing a drug delivery bag filled with a drug above the patient and letting gravity force the drug from the bag into the patient. Although this method has proven successful for many applications, its drawbacks included a) an unsteady flow to the patient due to the changing height of the intravenous infusion site relative to the drug bag, b) the awkwardness of requiring the patient to remain below the fluid delivery bag at all times, and c) the constant adjustment of a roller clamp which regulates the flow to the patient. Electromechanical infusion pumps were developed to mitigate these concerns. However, the utility of such pumps was hindered by their bulky size and by their need for a constant source of electricity. These hindrances are especially troublesome in situations where a patient is at home and ambulatory, thus requiring the freedom to move about.
During the past five years, a new style of apparatus has entered the marketplace for controlled delivery of a drug which does not require the use of an electromechanical infusion pump, and thus is suited for the controlled delivery of drugs to patients who are ambulatory. This new style utilizes an inflatable latex rubber balloon housed inside a rigid, clear plastic housing. When the devices are filled with a drug, the latex balloon expands. An administration set is attached to the device and thus acts as the conduit for the drug to the patient. When the balloon is inflated by the drug, the balloon itself becomes the driving force to transfer the drug out of the reservoir to the patient via the drug administration set. Controlled release of the drug at a desired flow rate is achieved by placing an orifice of predetermined diameter in the drug line. These devices generally operated at a relatively high pressures of approximately 10 to 15 psi. Examples of the latex balloon system are disclosed in U.S. Pat. Nos. 4,769,008 and 4,915,693 and European Patent Application 0,426,319 A2.
Although the latex balloon method of drug delivery has certain advantages over the electromechanical infusion pump, the method also has its disadvantages. For example, because the balloon expands in all directions, the shape of the housing enclosing the balloon is round. This round shape does not conform well to the patient when worn in the patient""s pocket. Furthermore, some of the latex balloon style devices require a special machine to fill and pressurize the balloon with a drug. Consequently, the pharmacist must use the special machine to load the device. Thus, there exists the need for a safe, economical drug delivery system which could (a) be inconspicuously and comfortably worn by the patient, (b) allow the pharmacist to fill the drug container without the use of a special pressurizing device, (c) allow the nurse or patient to load the drug container into the pressurizing device, (d) allow for reuse of parts of the system.
The present invention allows the use of standard, rectangular medication bags to be used in a platen pump. By using the standard bags, hospitals do not have to maintain a large inventory of medication bags of differing size and shape.
One aspect of the present invention is an infusion pump for expelling a fluid from a fluid reservoir. The infusion pump comprises a housing having a chamber therein for receiving a fluid reservoir and a first wall for contacting the fluid reservoir. A second wall is movable between a first position distanced from the first wall to form the chamber therebetween, and a second position relatively closer to the first wall. The second wall is moved by a parallelogram linkage. The parallelogram linkage comprises at least one spring for biasing the parallelogram linkage. The movement of the parallelogram linkage causes the second wall to advance toward the first wall. Importantly, the advancement of the second wall provides increased force on the fluid reservoir through the dispensation cycle thereby achieving a constant flow rate.
In another embodiment, the present invention is an infusion pump comprising a housing having a chamber therein for receiving a fluid reservoir. The pump contains a first wall for contacting the fluid reservoir and a second wall movable between a first position distanced from the first wall to form the chamber therebetween, and a second position relatively closer to the first wall. The pump includes a compression means for moving the second wall, wherein the compression means achieves a substantially constant flow rate from the fluid reservoir by increasing the force applied to the fluid reservoir as the second wall moves toward the second position.
In another embodiment, the present invention provides an infusion pump for expelling fluid from a flexible reservoir comprising a top shell, a bottom shell, a pressure plate, a shaft, a first slide, a second slide, four arms, and a biasing means. The top shell is removably connected to the bottom shell, the bottom shell having a non-planar interior bottom surface. The pressure plate is movably connected to the top shell. The plate has a non-planar surface complementary to the interior bottom surface of the bottom shell. A variable-sized area is defined between the pressure plate and the interior bottom surface of the bottom shell, the area generally capable of accepting the fluid reservoir therein. The shaft is positioned between the top and bottom shells, and has a first end and a second end. The first and second slides are slidably positioned on the shaft. The four arms define a parallelogram structure extending between the top shell, the first slide, the second slide, and the pressure plate. The arms are rotatably connected to the top shell, the slide members, and the pressure plate. The slide members and shaft are supported by the arms between the shells. The biasing means are positioned between the first end of the shaft and the first slide, and between the second end of the shaft and the second slide, for biasing the slides toward one another along the shaft, thereby biasing the pressure plate through the arms, downwardly towards the bottom shell when the top and bottom shells are connected.
In yet another embodiment, the present invention provides an infusion pump for expelling fluid from a fluid reservoir, comprising a housing, a platen member, first through fourth arms, and first and second springs. The housing comprises a bottom member having a non-planar inner surface and a top member removably connected to the bottom member. The platen member is movably connected to the top member. The platen has a non-planar engaging surface which is complementary in shape to the inner surface of the bottom member. The first arm has a first end and a second end, the first end rotatably connected to the top member and the second end rotatably connected to a first mounting block. The second arm has a first end and a second end, the first end rotatably connected to the top member and the second end rotatably connected to a second mounting block. The shaft has a first end and a second end and extends through the blocks. The first spring extends between the first end of the shaft and the first block. The second spring extends between the second end of the shaft and the second block. The third arm has a first end and a second end, the first end rotatably connected to the first block and the second end rotatably connected to the platen member. The fourth arm has a first end and a second end, the first end rotatably connected to the second block and the second end rotatably connected to the platen member. The arms form a linkage between the top member, the blocks, and the platen member, biasing the platen member downwardly towards the bottom member when the top and bottom members are connected.
Further features and advantages of the present invention will become apparent to one of skill in the art from a review of the Detailed Description of Preferred Embodiments which follows, when considered with the attached claims and drawings.